In recent years, in a motor drive apparatus for an automobile or an industry, in order to remove or miniaturize a harness connecting a motor to a power conversion device, mechatronical integration has progressed in which the motor and the power conversion device are built into a common casing, or a casing is directly connected thereto. In this mechatronical integration mounting structure, a noncontact sensor or the like starts to be used in order to reduce the number of contacts of electrical wirings between the motor and the power conversion device. A magnetic sensor such as a hole element or an MR element is frequently used instead of a resolver of the related art as a noncontact position sensor for detecting a rotor position of a motor.
For example, PTL 1 discloses a system using a magnetic sensor. PTL 1 discloses a rotation angle measurement device which includes a magnetic sensor responding in a magnetic field direction, and a detection unit receiving output from the magnetic sensor; the rotation angle measurement device is used along with a rotor having a magnetic flux generation member; the output from the magnetic sensor is an original angle signal set corresponding to the magnetic field direction; and the detection unit outputs a correction angle in which the influence of a nonmagnetic conductor disposed near the magnetic sensor is corrected by using a correction value which is output by a correction function having a rotation speed of the rotor as an argument.
In recent years, as a result of high density mounting of a power conversion device for realizing mechatronical integration, a main circuit wiring via which a power source is electrically connected to the motor and which causes a current for driving the motor to flow is disposed near the above-described magnetic sensor.
PTL 2 discloses an example of a motor drive apparatus with high density. PTL 2 discloses a motor including a stator on which a plurality of winding wires are wound; a rotor rotatably disposed within an inner radius of the stator; a shaft coaxially disposed to be rotatable with the rotor; a magnet disposed on one end of the shaft to be rotatable with the rotor and the shaft; a magnetic sensor disposed to face the magnet in an axial direction of the shaft for detecting a rotation angle of the rotor by sensing the magnetism generated by the magnet; a control device controlling power supplied to each of the winding wires on the basis of the rotation angle of the rotor detected by the magnetic sensor; and a first conducting wire and a second conducting wire respectively intersecting a virtual circle centering on an axis of the shaft and respectively extending in parallel with the axis of the shaft, for connecting the control device to each of the plurality of winding wires, in which a current flowing through each of the first conducting wire and the second conducting wire has the same magnitude and the same flow direction as each other at any point of time, and a position of the first conducting wire and a position of the second conducting wire satisfy a relationship α=180, when an intersection of the first conducting wire with the virtual circle is designated as a point p1, and an intersection of the second conducting wire with the virtual circle is designated as a point p2, and a central angle of an arc p1p2 of the virtual circle is designated as α(°).
Here, the content disclosed in PTL 1 relates to a method of reducing the influence of an eddy current generated in a metal disposed near the magnet exerted on the magnetic sensor by rotating the position detection magnet at a high speed. However, for example, a main circuit wiring made of copper is disposed as a nonmagnetic body disposed near the position sensor, and it is not possible to reduce the influence that magnetic flux generated on the basis of the Biot-Savart law when a current flows through the main circuit wiring exerts on the magnetic sensor.
On the other hand, according to the content disclosed in PTL 2, in six motor wires connected to two three-phase inverters, motor coils connected to the six motor wires are disposed in the same casing. The system detecting a position of the rotor with the magnetic sensor has a structure in which two motor wires having the same phase centering on the magnetic sensor are opposite to each other by 180°. In the above-described arrangement, a magnetic flux vector generated when a current flows through one motor wire and a magnetic flux vector generated when a current with the same magnitude and direction flow through the other motor wire cancel out each other at a detection point of the magnetic sensor, and thus the influence of magnetic flux generated when a current flows through the main circuit wiring can be reduced. However, in the aspect disclosed in PTL 2, in a case where one inverter fails, and an operation is continuously performed with only the other inverter, magnetic flux generated from the other motor wire cannot be canceled out at a detection point in the magnetic sensor, and thus there is a problem in which position detection accuracy deteriorates, and thus motor control is unstable.